1. Field of the Invention
This invention relates generally to three dimensional coordinate measuring machines (or CMM's). More particularly, this invention relates to a new and improved three dimensional CMM which is convertible between two or more arm configurations.
2. Prior Art
It will be appreciated that everything in the physical world occupies volume or space. Position in a space may be defined by length, width and height which, in engineering terms, is often called an X, Y, Z coordinate. The X, Y, Z numbers represent the dimensions of length, width and height or three dimensions. Three-dimensional objects are described in terms of position and orientation; that is, not just where an object is but in what direction it points. The orientation of an object in space can be defined by the position of three points on the object. Orientation can also be described by the angles of alignment of the object in space. The X, Y, and Z coordinates can be most simply measured by three linear scales. In other words, if you lay a scale along the length, width and height of a space, you can measure the position of a point in the space.
Presently, coordinate measurement machines or CMM's measure objects in a space using three linear scales. FARO Technologies, Inc. of Lake Mary, Fla. (the assignee of the present invention) has successfully produced a series of electrogoniometer-type digitizing devices for the medical field. In particular, FARO Technologies, Inc. has produced systems for skeletal analysis known as METRECOM.RTM. and systems for use in surgical applications known as SURGICOM.TM.. Electrogoniometer-type devices of the type embodied in the METRECOM and SURGICOM systems are disclosed in U.S. Pat. Nos. 4,760,851, 5,251,127 and 5,305,203, all of which are assigned to the assignee hereof and incorporated herein by reference.
Portable CMM's are now used for three dimensional measurement of objects for reverse engineering, inspection, etc. An exemplary portable CMM system is disclosed in U.S. Pat. No. 5,402,582 assigned to the assignee ofthe present application, and which is incorporated herein by reference. As shown in FIG. 1, the three dimensional measuring system of U.S. Pat. No. 5,402,582 generally comprises a coordinate measuring machine (CMM) 10 composed of a manually operated multijointed arm 12 and a support base or post 14, a controller or serial box 16 and a host computer 18. It will be appreciated that CMM 10 electronically communicates with serial box 16 which, in turn, electronically communicates with host computer 18.
As will be discussed in more detail hereinafter, CMM 10 includes transducers (e.g., one transducer for each degree of freedom) which gather rotational positioning data and forward this basic data to serial box 16. Serial box 16 provides a reduction in the overall requirements of host computer 18 to handle certain complex calculations and provides certain preliminary data manipulations. The serial box 16 includes EEPROMS which contain data handling software, a microcomputer processor, a signal processing board and a number of indicator lights 20. As mentioned, basic transducer data is sent from CMM 10 to serial box 16. Serial box 16 then processes the raw transducer data on an ongoing basis and responds to the queries of the host computer with the desired three-dimensional positional or orientational information.
As shown in FIG. 2, the CMM 10 comprises a base 14 connected to a first set of two transfer housings including a first transfer housing 40 which, in turn, is connected to a second transfer housing 42 (positioned transverse to housing 40). A first extension member 44 is rigidly attached to a second set of two transfer housings including a third transfer housing 46 transversely attached to a fourth transfer housing 48. First extension member 44 is positioned perpendicularly between transfer housings 42 and 46. A second extension member 50 is aligned with and rigidly attached to transfer housing 48. Rigid extension member 50 is rigidly attached to a third set of two transfer housings including a fifth transfer housing 52 transversely attached to a sixth transfer housing 54. Fifth transfer housing 54 has attached thereto a handle/probe assembly 56 at the end of the multijointed arm. Additional details of the CMM 10 are disclosed in U.S. Pat. No. 5,402,582 which is incorporated herein by reference.
The CMM systems of the prior art are well suited for their intended purposes. There are, however, drawbacks to these prior designs. One disadvantage is the inability to alter the number of degrees of freedom of the multijointed arm. In addition, it is often difficult to see the display on the serial box and hear audible tones produced by the serial box. Accordingly, there is a continuing need for improved, accurate and low cost CMM's for industrial and related applications.